The present invention relates to alloys to be used as at least one lead member for an electric lamp that requires at least one metal/vitreous material junctions, and to electrode structures of the electric lamp. The vitreous material is quartz or a high temperature glass, for example aluminosilicate glass.
The material and the configuration of an electric conductor, a current conductor, or a lead member of an electric lamp having a vitreous or a glass envelope, has great effect on the structure, the function, and the quality of the electric lamp. The term “electric lamp” in this case includes various halogen incandescent lamps as well as electric discharge lamps, such as a high pressure mercury lamp, a metal halide lamp, or a high pressure xenon lamp. In addition, the term “lead member” may include a wide variety of leads, for example, a lead film, a lead foil, a plate, or the like.
This technological field has received much attention for a long time. A conductor for supplying an electric current to a gas-filled or a non-gas-filled electric lamp is generally sealed and joined by melting a quartz or a high temperature glass. Therefore, molybdenum and tungsten are used as a material for the current conductor because these melting point is high in all metals, these thermal expansion coefficient close to that of the vitreous materials.
Other characteristics required for molybdenum or tungsten as a conductor material include excellent ductility, excellent plasticity, high mechanical strength, oxidation resistance, corrosion resistance (particularly against halides), and excellent weldability with other conductor materials.
For example, German Patent DE 3006849 discloses that corrosion resistance is improved by coating an electric conductor comprising a molybdenum or tungsten foil with a secondary metal such as tantalum, niobium, vanadium, chromium, zirconium, titanium, yttrium, lanthanum, scandium or hafnium, using methods such as evaporation, cathode sputtering, electrolysis, and various other techniques.
Further, in order to produce an electric lamp using a material suitable as a current conductor foil, German Patent DE 2947230 proposes to use a novel molybdenum foil obtained by dispersing 0.25 to 1% yttrium oxide particles in an existing molybdenum foil.
Further, U.S. Pat. No. 5,021,711 proposes ion implantation of chromium, aluminum, or a combination of these metals in a surface layer of the molybdenum foil used as a current conductor within a vacuum bulb in order to improve the oxidation resistance of the molybdenum foil and to protect the molybdenum foil from oxidation.
Further, European Patent 0309749 proposes a technique in which molybdenum, which is used as a current conductor of an electric lamp, is coated in a seal area of the electric lamp with alkali metal silicate so as to improve oxidation resistance of molybdenum within an oxidizing atmosphere and at a high temperature of 250° C. to 600° C.
Further, Japanese Patent Application Publication (JP-A) No. 2002-33079 discloses a method of producing an electric light. In the disclosed method, a molybdenum foil is subjected to after-treatment so that heterogeneous surface structures and/or substantially non-contiguous insular regions of agglomerates of molybdenum or an alloy thereof are formed on 5 to 60% of the surface area of the molybdenum foil at a vapor pressure of in each case less than 10 mb (10 hPa) and at a temperature of 2000° C.
Further, Japanese Patent Application Publication (JP-A) No. 2001-06549 discloses a method of producing an automobile light bulb, incorporating a primary pinch-sealing method. An electrode assembly comprising an electrode rod, a molybdenum foil, and a molybdenum external lead connected in series is inserted through one end of a glass tube. An anti-oxidant gas is introduced through the other end, and temporary pinch-sealing is performed. Then, main pinch-sealing is performed under low pressure.
Further, Japanese Patent Application Publication (JP-A) No. 2001-23572 discloses a secondary pinch-sealing method. In the disclosed method, an electrode assembly is sealed and joined after introducing light-emitting substances and a discharge starting gas into a work which has been pinch-sealed by primary pinch-sealing.
However, industrial implementation of the coating in German Patent DE 3006849 is disadvantageous in that the manufacturing cost is high, a uniform thickness is difficult to obtain, and desired anti-corrosion effect is not obtained. Further, the coated electric conductor is inferior in weldability.
Further, the molybdenum foil disclosed in German Patent DE 2947230 is insufficient in corrosion resistance, particularly in oxidation resistance.
Further, the molybdenum foil disclosed in U.S. Pat. No. 5,021,711 is insufficient in weldability and requires much labor and cost, resulting in a marked increase in manufacturing cost of mass production of quartz bulb lamps.
Further, the current conductor wire provided with the coating layer as disclosed in Europe Patent EP 0309749 is disadvantageous in that the relatively costly method is required. Specifically, coating is carried out after welding. Therefore, the manufacturing cost is high and the brittleness is increased so that the parts are easily broken.
Further, in order to form the substantially non-contiguous insular regions of agglomerates as disclosed in Japanese Patent Application Publication (JP-A) No. 2002-33079, a new process must be added. This results in a problem of a markedly increase in manufacturing cost of mass production. In addition, it is necessary to highly sensitively control the manufacturing process, for example, to highly precisely control the surface condition for the surface area of 5 to 60% and to controllably suppress the average dimension of the agglomerates to 5 μm or less.
It is noted here that the alloy for a lead member of the present invention is used as a current conductor, an electric conductor, and a current conductor wire of an electric lamp, which may collectively be referred to as a “current conductor” hereinafter.